1. Field of the Invention
The present invention relates to an organic EL element.
2. Description of the Related Art
In an organic electroluminescence (EL) element, an electric field is applied to an organic fluorescent compound so as to be excited to emit light. Characteristics of the organic EL element include self-illumination, a wide viewing angle, a high response speed, a low driving voltage, and full color. The organic EL element has currently been put to practical use, and may apply to a flat color display device such as a compact display panel, an out-door screen, or a screen for a personal computer or a television set.
The organic EL element has a structure in which an organic layer having a luminescence characteristic is interposed between two electrodes. When a DC voltage is applied to the two electrodes, a hole is injected from a positive electrode to the organic layer, and an electron is injected from a negative electrode to the organic layer. According to the electric field generated in response to the applied voltage, these carriers are transferred inside an organic emission layer, and thereby carrier recombination occurs.
A part of energy emitted when the electron and the hole are recombined is used to excite a luminescent molecule. When the excited luminescent molecule emits energy and thus returns to a ground state, a certain portion of the energy is emitted in the form of a photon. This is an emission principle of the organic EL element.
When manufacturing the organic EL element, a driving element such as a TFT, which is used to drive the organic EL element, a conductive pattern and the like are formed on a substrate (i.e., a glass substrate), and then they are covered by a flattening film. Thereafter, a first electrode, an insulation layer, an emission layer, and a second electrode are formed in this order on the flattening film.
However, while the first electrode is subjected to the above processes, process damage may occur, or dust may be attached onto the first electrode. This affects to a characteristic of the organic EL element, which leads to deterioration in emission quality.
To cope with the above problem, a technique has been proposed in which the organic EL element is produced by sequentially laminating a first electrode, a protection film, an emission layer composed of an organic material, and a second electrode on a substrate, and by removing the protection film existing in a pixel area on the first electrode before the emission layer is laminated (Japanese Unexamined Patent Publication No. 2001-185363). According to this technique, the protection film has a film thickness of 1 μm, and the organic layer has a film thickness of 1,250 Å, where the film thickness of the protection film is greater than that of the organic layer.